An ink jet printer is equipped with an ink jet head that forms desired dots on printing paper by discharging ink from its nozzles toward the paper. For example, FIG. 1 of Japanese Patent Application Laid-open No. 04-341852 corresponding to U.S. Pat. No. 5,402,159 shows such an ink jet head which is provided with ink channels and actuators. The ink channels extend from a manifold, which holds ink, each via a pressure chamber to a nozzle. Each of the actuators develops pressure in one of the pressure chambers by changing the volume of the chamber. Since the ink channels are filled with ink supplied from the manifold, the development of pressure in the pressure chambers causes pressure waves through the medium of the ink in the ink channels, and the pressure waves propagate through the pressure chambers. The pressure developed in the pressure chambers raises the pressure near the nozzles, and the discharge of ink begins. When negative pressure waves propagating from the manifold reach the vicinities of the nozzles, the pressure near the nozzles falls, and the ink discharge ceases.
In order to attain the desired print concentration, ink droplets having the predetermined volume must be discharged from the nozzles. The volume of an ink droplet discharged from a nozzle depends on the area of the nozzle opening, the speed at which the ink droplet is discharged from the nozzle, and AL (acoustic length) that is the length of time for a pressure wave to propagate from the manifold to the nozzle. In order to discharge ink droplets of the predetermined volume, it is conceivable to enlarge the area of the nozzle opening, raise the discharge speed of the ink droplets, or increase the AL. However, enlarging the opening area increases the driving voltage required for discharging the ink droplets, leading to the problem of greater power consumption of the actuator. Enlarging the opening area also gives rise to the problem of ink that fills the ink channel leaking from the nozzle when the ink jet head is subjected to even a slight vibration. Raising the discharge speed of the ink droplets requires that the volumetric change of the pressure chamber, that is, the displacement of the actuator, be increased. In order to increase the actuator displacement, a higher voltage must be impressed across the actuator, leading to an increase in power consumption of the actuator during ink discharge.
In order to increase the AL, it is conceivable to enlarge the pressure chamber. However, doing so requires an increase in the volumetric change of the pressure chamber in order to create an equivalent pressure in the chamber. This in turn requires a bigger actuator or an increase in the drive amount of the actuator. In any case, the result is an increase in the power consumption of the actuator during ink discharge. The production cost of electrical components for driving the actuators also rises accordingly. Enlarging the pressure chambers lowers the degree of integration of the ink channels. This not only increases the size of the ink jet head but also widens the nozzle spacing, posing difficulties for fine printing. From the standpoint of reducing the nozzle spacing for fine printing, it is preferable that the pressure chambers be narrow and long and extend from the manifold toward the respective nozzles. This reduces the nozzle spacing in a direction perpendicular to the direction in which the pressure chambers extend. However, the narrow and long pressure chambers reduce the efficiency of the actuators in changing the volume of the pressure chambers. Consequently, in order to attain the predetermined volumetric change, a higher voltage must be supplied to the actuators, leading to increased power consumption of the actuators during ink discharge.
Japanese Patent Application Laid-open No. 05-162311 discloses an ink jet pressure generation chamber (1) provided with an ink discharge nozzle (2). An ink supply channel (3) is tangent to the peripheral wall of the pressure generation chamber (claim 1 and FIG. 1). This publication discloses other ink jet pressure generation chambers (1), each of which is fitted with an ink discharge nozzle (2) and a deflection plate (7). Ink flows from an ink supply channel (3) into the pressure generation chamber. The deflection plate causes the ink from the supply channel to flow vortically in the pressure generation chamber (claim 2 and FIGS. 7 and 8).